傳遞一個代表回調到本地C++ API調用

Question

有人能指出我什麼是錯與此代碼嗎？我在混合使用C++和MC++方面有非常艱苦的經驗。我已經閱讀了很多有關這個主題的博客和教程（通過代表），但現在看起來我的代碼是好的（編譯並且在調試模式下一步一步地運行良好）會崩潰。

的主要問題是，它需要有一個代表是一個成員函數（其需要訪問其他類成員）。

我記得那裏有waveInProc文檔中的一張紙條，上面說，回調中你不能調用任何系統功能。應該是因爲它試圖使用其他成員，並且託管環境發生在這裏調用其他系統方法，所以應用程序崩潰了？

ref class CWaveIn 
{ 
public: 
void CWaveIn::Open(int currentInputDeviceId) 
private: 
void AllocateBuffer(void); 
void WaveInProc(HWAVEIN hwi, UINT uMsg, DWORD_PTR dwInstance, DWORD_PTR dwParam1, DWORD_PTR dwParam2); 
delegate void CallBack(HWAVEIN hwi, UINT uMsg, DWORD_PTR dwInstance, DWORD_PTR dwParam1, DWORD_PTR dwParam2); 
CallBack^ myDelegate; 
protected: 
WAVEFORMATEX* waveFormat; 
int bufferDuration; // in seconds 
BYTE* waveInBuffer; 
int bufferSize; 
}; 

void CWaveIn::AllocateBuffer(void) 
{ 
free(waveInBuffer); 
bufferSize = waveFormat->nAvgBytesPerSec * bufferDuration; 
waveInBuffer = new BYTE[bufferSize]; 
Debug::WriteLine("BufferSize: " + bufferSize); 
} 

void CWaveIn::WaveInProc(HWAVEIN hwi, UINT uMsg, DWORD_PTR dwInstance, DWORD_PTR dwParam1, DWORD_PTR dwParam2) 
{ 
switch(uMsg) { 
    case WIM_CLOSE: 
    Debug::WriteLine("WIM_CLOSE"); 
    break; 
    case WIM_DATA: 
    for(int i=0;i<bufferSize; i++) { 
    Debug::Write(waveInBuffer[i] + " "); 
    } 
    Debug::WriteLine("WIM_DATA"); 
    break; 
    case WIM_OPEN: 
    Debug::WriteLine("WIM_OPEN"); 
    break; 
} 
} 

void CWaveIn::Open(int currentInputDeviceId) 
{ 
MMRESULT result = ::waveInOpen(0, currentInputDeviceId, waveFormat, 0, 0, WAVE_FORMAT_QUERY); 
Debug::WriteLine(L"CWaveIn::Open() WAVE_FORMAT_QUERY: device " + currentInputDeviceId.ToString()); 
DebugError(result); 
if(result == MMSYSERR_NOERROR) 
{ 
    myDelegate = gcnew CallBack(this, &CWaveIn::WaveInProc); 
    pin_ptr<CallBack^> ptrMyDelegate= &myDelegate; 
    IntPtr delegatePointer = System::Runtime::InteropServices::Marshal::GetFunctionPointerForDelegate(myDelegate); 

    HWAVEIN hWaveIn; 
    MMRESULT result = ::waveInOpen(&hWaveIn, currentInputDeviceId, waveFormat, (DWORD_PTR)delegatePointer.ToPointer(), 0, CALLBACK_FUNCTION | WAVE_FORMAT_DIRECT); 
    Debug::WriteLine(L"CWaveIn::Open() : device " + currentInputDeviceId.ToString()); 
    DebugError(result); 

    AllocateBuffer(); 

    WAVEHDR WaveInHdr; 
    WaveInHdr.lpData = (LPSTR)waveInBuffer; 
    WaveInHdr.dwBufferLength = bufferSize; 
    WaveInHdr.dwBytesRecorded=0; 
    WaveInHdr.dwUser = 0L; 
    WaveInHdr.dwFlags = 0L; 
    WaveInHdr.dwLoops = 0L; 
    ::waveInPrepareHeader(hWaveIn, &WaveInHdr, sizeof(WAVEHDR)); 
    result = ::waveInAddBuffer(hWaveIn, &WaveInHdr, sizeof(WAVEHDR)); 

    result = ::waveInStart(hWaveIn); 
    Debug::WriteLine(L"CWaveIn::Start() : device " + currentInputDeviceId.ToString()); 
    DebugError(result); 
} 
} 

Answer 1

您的聲明在託管堆中pin_ptr，然後你把它傳遞給一個未管理功能 所有這個指針管理引用內部CWaveIn::Open(int currentInputDeviceId) 所以我想GC認爲沒有理由把這個對象在CWaveIn::Open之後退出。

嘗試在類範圍，而不是函數範圍

Answer 2

你需要使用一個的GCHandle而非pin_ptr創建它。見http://msdn.microsoft.com/en-us/library/367eeye0(v=vs.80).aspx